Thermoplastic molding compositions containing polycarbonate and polyalkylene terephthalate are known. Many such compositions have been disclosed in the patent literature. Mention may be made in this context of U.S. Pat. No. 4,888,388 which disclosed an impact resistant thermoplastic composition having distinguished surface appearance, color stability and thermal stability. The composition contains a particular graft rubber copolymer, polycarbonate and saturated polyester. A self extinguishing polycarbonate composition, stabilized against degradation and containing a halogenated phosphorous compound has been disclosed in U.S. Pat. No. 3,557,053. Also known are compositions which contain phosphorous compounds as additives, primarily as flame retarding agents. The combination of phosphorous compounds with halogenated additives has been disclosed to impart flame resistance to thermoplastic compositions. U.S. Pat. No. 5,276,077 is noted in this connection for its disclosure of an ignition resistant composition which contains polycarbonate, rubber modified monovinyl-idene aromatic copolymer and a rubbery core/shell graft copolymer impact modifier.